(57) A lateral bipolar transistor formed on a silicon on insulator (SOI) substrate, having a base electrode of heat resistive polycrystalline silicon of first conductivity type, formed on a base region of first conductivity type, all the bottom plane of the transistor region is in contact with the insulating layer of the SOI substrate. The base electrode is extended laterally over a part of a collector region to provide a relatively large base electrode width, which allows a small width of the base region, enhancing the current amplification factor of the transistor. The base region has a vertical doping profile which has a minimum value between the base electrode and the insulator layer of the substrate, reducing the recombination of carriers in the base region. Fabricating methods utilizing self-alignment-diffusion process are provided.